Single action timing circuit



Dec. 31, 1957 M. 1.. AITEL v 2,818,532

SINGLE ACTION-TIMING xgcurr Filed Nov. 1, 1955 2 Sheefns-Sheet 1INVENTOR. Mm; L. AITELI ATTORNEY 1957 M. L. AlTEL 2,818,532

SINGLE ACTION TIMING CIRCUIT Filed Nov. 1. 1955 2 Sheets-Sheet 2 IN V ENTOR.

? [4 6. M05 L-AITELI ATTORNEY SINGLE ACTION TIMING CIRCUIT Moe LawrenceAitel, Haddon Heights, N. J., assignor to Radio Corporation of America,a corporation of Delaware Application November 1, 1955, Serial No.544,228

17 Claims. (Cl. 315-234) This invention relates to timing circuitdevices, and more particularly to a single action timing circuit.

It is often desirable to have a work circuit that operates for apredetermined period of time, or that starts after a predetermineddelay. Such circuits find application in photography, electronics,material handling, etc. Various applications of such circuits in thesefields include, for example, timing exposures in photography; inelectronic circuits, applying anode current a fixed time afterconnecting cathode heaters, and, in material handling, utilizing theweight or movement of an object to trigger an operation of preset timeduration.

It is often advantageous to have the timing circuit operate through agiven time interval substantially inde pendent of the time duration ofthe triggering impulse. Further, it is often desirable that the circuitremain in a quiescent or inoperative condition at the end of the giveninterval until the trigger is released or reset, without any otherresetting action being required.

Circuits of the prior art have accomplished one or more of these resultsby using many resistors, capacitors, vacuum or gas filled tubes, relays,and other circuit components. Attempts at simplification of the circuitsand the consequent reduction in the number of elements often haveresulted in the sacrifice of one or more of the features of activationindependent of trigger duration, single action operation, or reset bythe reset of the trigger.

Accordingly, it is an object of this invention to provide an improvedvariable timing circuit for control purposes that is simpler than thecircuits of the prior art.

Another object of the invention is to provide an improved timing circuitthat will operate only once when triggered.

It is a further object of this invention to provide an improved, singleaction timing circuit wherein the interval timed may be readily varied.

A still further object of the present invention is to provide animproved timing circuit that will operate for a fixed time intervalsubstantially independent of the time duration of the trigger influence.

An additional object of this invention is to provide an improved, singleaction timing circuit that will be reset only upon release of thetrigger.

Circuits embodying the present invention have three operating states,which may be termed dwell, working, and quiescent states. Initially, thecircuit may be in a dwell state in which the trigger is set. Actuationof the trigger during the dwell state initiates the second, or working,state. At the conclusion of the timing interval, the circuit assumes aquiescent state which resembles the first state except that the circuitwill not work again until the trigger is released or reset.

According to the present invention, a resistor and capacitor in seriesare connected in parallel with a thyratron or other multi-element,gas-filled tube with the capacitor on the cathode side of the parallelcircuit. The control electrode or grid is, coupled to the junction ofthe resistor and capacitor and is connected to a negative potentialsource. During the dwell state, a trigger impulse causes the controlgrid to be disconnected from the negative potential source, therebystarting the timed interval, which constitutes the working state. Thecapacitor then charges toward the potential of the thyratron anode. Thecircuit parameters determine the charging time for the capacitor. Theend of the timed interval and the working state occurs when the grid issufficiently raised in potential to fire the tube, and the circuitenters its quiescent state. Releasing the trigger extinguishes the tubeand resets the circuit to the dwell state. A relay is included in theanode circuit. The one set of relay contacts may control the grid bias.In one form of the invention, a second set of relay contacts may be usedto prevent premature termination of the timed interval should thetrigger be released during the Working interval.

The timing circuit may operate an external work circuit by connecting aload through the relay contacts. Alternatively, the relay may energize awork system mechanically. Should an electrical signal be desired, asuitable impedance may be included in the timing circuit to provide apulse, or a signal of desired level or waveform for the duration of theworking state.

The novel features of the invention, as well as the invention itself,both as to its organization and method of operation, will best beunderstood from the following description when read in connection withthe accompanying drawings, in which:

Fig. 1 is a diagram of a circuit embodying one form of the presentinvention;

Fig. 2 is an alternate form of the circuit of Fig. 1 in which the relaywinding is not included in the charging circuit;

Fig. 3 is a modification of the embodiment of Fig. l, in which anadditional relay contact switch is included in the relay to preventpremature termination of the working period;

Fig. 4 is an alternate form of a circuit including the invention inwhich an additional relay contact switch is added to the circuit of Fig.2 for a like purpose;

Fig. 5 is a further embodiment of the present invention in which therelay is energized only during the Working period;

Fig. 6 is an alternate form of the circuit of Fig. 5 in which a bias isapplied to the relay toprevent energization thereof while the thyratronis conducting; and

Fig. 7 is a voltage divider network which may be used in the circuit ofFig. 6.

A common reference potential to which all voltage levels are referred isindicated by the conventional ground symbol 14. Sources of potential areindicated by conventional battery symbols appropriately connected,although any suitable source of power may be used.

In the circuit of Fig. 1., one terminal of the winding of a relay 10 isconnected to the positive terminal of a source of potential 12, thenegative terminal of which is connected to ground 14. The other terminalof the winding of the relay 10 is connected to ground 14 through atrigger switch 16. Also connected to the relay 10, in a circuit parallelwith the trigger switch 16, is the anode 18 of a thyratron 20. Thethyratron cathode 22 is connected to ground 14. The thyratron grid 24 isconnected to ground 14 through a capacitor 26. The negative termimat ofa bias potential source 28 is connected through a contact switch 30controlled by the relay 10 and a switch current limiting resistor 32 tothe thyratron grid 24 at. the junction with the capacitor 26. Thepositive terminal. of the bias source 28 is connected to ground 14. Avariable resistor 34 in series with a fixed resistor 36 connects thegrid 24 to the anode 18. The anode to cathode circuit of the thyratron20 comprises the parallel 3 combination of the switch 16 and the seriescombination of the resistors 34, 36 and the capacitor 26.

In operation, the relay is normally energized in the dwell state bycurrent flow from the positive source 12, through the relay 10 winding,and thence through the trigger switch 16 to ground 14. The thyratron 20has its anode 18 and cathode 22 at ground potential because of the shortcircuit path through the trigger switch 16. The thyratron grid 24 isbiased to a negative value by the negative source 28 and the capacitor26 is charged to that negative value. The combined resistance of thefixed resistor 36 and the variable resistor 34 is very large, that is,ten times as large or more, compared to the resistance of the resistor32 alone.

The trigger switch 16 may be of any suitable type, such as a relayresponsive switch which may he opened 1n response to a trigger impulsefrom an external source (not shown). When the switch 16 is opened, therelay 10 is de-energized, thus starting the working period. The closedrelay contact 30 opens, disconnecting the thyratron grid 24 from thenegative source 28. At the same time, the potential of the anode 18 ofthe thyratron 20 rises to the value of the positive source 12. Thecapacitor 26 is now charged toward the potential of the positiveterminal of the source 12 through the combined resistors 34 and 36 andthe winding of the relay 10 which, of course, also has some resistance.The time constant of the combination of the relay winding, the fixedresistor 36, and the capacitor 26 largely determines the minimumcharging time for the capacitor 26. The variable resistor 34 may beadjusted to vary the time interval by varying the total resistance ofthe resistor-capacitor combination. The thyratron grid 24 potentialrises as the capacitor 26 is charged and, when the potential of the grid24 is sufficiently positive, the thyratron 20 is fired. The relay 10,now a part of the anode circuit of the thyratron 20, is energized. Therelay contact switch 30 is now closed by the energized relay 10, therebyterminating the dwell state. The negative source 28 is then reconnectedto the thyratron grid 24 and capacitor 26, the capacitor 26 againcharging to the bias voltage. The thyratron will continue to conduct,leaving the circuit in the quiescent state, until the trigger switch 16is closed, thereby once again connecting the thyratron cathode 22 to thethyratron anode 18.

In the circuit of Fig. 2, the resistors 34 and 36 are connected directlyto the positive source 12, eliminating the relay winding 10 from thecharging circuit. However, the operation of the circuit is sufiicientlysimilar to that described above for the circuit of Fig. 1 so thatfurther description is unnecessary for those skilled in the art.

A premature closing of the trigger switch 16 in the circuits of Fig. 1and Fig. 2 will re-energize the relay 10 before the predetermined timeinterval has elapsed. Thus, in efiect, the working state is prematurelyterminated. In some applications, this efifect is undesirable. Thiseffect may be avoided by the circuits of Figs. 3 and 4 which include asecond contact switch 38 which is controlled by the relay 10. In each ofthese circuits, this second relay switch 38 is placed in series with thetrigger switch 16. The contact switch 38 remains open during the timethat the relay 10 is de-energized. Hence, reclosing the trigger switch16 before the completion of the timed interval has no eltect on thecircuit.

In Fig. 5, an alternative form of the invention is shown in which arelay operates only during the timed working interval. The relay 10 isplaced in parallel with the thyratron 20 and an additional resistor 40is added in series with this parallel combination. Preferably, theresistance of resistor 40 is of the same order (has a value within afactor of ten) of the resistance of the winding of the relay 10. Boththese values should be great enough so that the voltage across the relay10, when the thyratron 20 is non-conductive, is sufficient for reliablefiring of'the thyratron, and the operating voltage of the thyratron,when conductive, is too low to mamtain the relay 10 energized. In thecircuit of Fig. 5, the parallel circuit of the trigger switch 16 withthe relay contact switch 38 connects the resistor 40 to the positivesource 12. In the dwell state, the switches 16 and 38 are opened andcurrent flows from the positive source 12 through a circuit whichincludes the fixed resistor 36, the variable resistor 34, the currentlimiting resistor 32, and the normally-closed relay contact 30 to thenegative source 28. The thyratron grid 24, as before, is connected toground 14 through the capacitor 26, to the source of negative supply 28through the resistor 32 and the switch 30, and, through the seriesresistors 34 and 36, to the positive source 12. Therefore, in the dwellstate of the circuit, the capacitor 26 is charged to the negativepotential and the circuit is ready for operation. Closing the triggerswitch 16 provides a shunt path for the current flow through theresistor 40 and the relay 10. The relay 10 is thus energized and thecontact switch 38 closes. The contact switch 30 opens and the capacitor26 starts to charge toward the positive potential level through theresistors 34 and 36. The thyratron grid 24 becomes more positive duringthe working time interval, which is terminated by the firing of thethyratron 20. The impedance of the thyratron 20 is sufliciently low toshunt the current away from the relay 10. Current flow in the relay 10is then insufficient to maintain energization thereof. The relay 10therefore becomes de-energized. Relay contacts 30 thereupon close andcontacts 38 open. The circuit is now in the quiescent state, the relay10 being de-energized. When the trigger switch 16 is re-opened, thethyratron 20 is open-circuited and thus extinguished.

During conduction of the thyratron 20, the current flow through therelay 10 must be kept sufficiently small to prevent energization of therelay 10. Rather than rely upon the relative values of the resistance ofthe relay winding 10, the resistor 40, and the thyratron 20, a source ofpositive supply 42 may be introduced into the circuit between the relay10 and ground 14, as shown in Fig. 6. This source of supply 42 acts tooppose any current flow through the relay 10.

Fig. 7 is a diagram of a voltage divider circuit which may be used toreplace the source of supply 42 in the circuit of Fig. 6. A resistor 50is tapped at the junction 46' to produce a potential equivalent to thatof the potential source 42 and may be introduced into the circuit ofFig. 6 at the junction 46. Similarly, the resistor 50 may be connectedat the positive supply side by connecting the junction 44' of Fig. 7 tothe junction 44 of Fig. 6.

In one form of the embodiment of Fig. 1, the circuit components had thefollowing illustrative values: These values are advisory only and anyperson skilled in the art should be able to select components of valuessuitable for any particular application. In this one form of thecircuit, the fixed resistor 36 had a value of .13 mcgohrn. The variableresistor 34 had a range from 0 to 2.5 megohms. The positive voltage ofthe source 12 was forty-eight volts and the negative voltage of thesource 28 was 22.5 volts. The capacitor 26 had a value of 1 fd. With afour-element gas-filled thyratron commercially available and designatedas 2D21, the time interval varied from 50 milliseconds to one second byadjustments of the variable resistor.

As may be seen, a simple, inexpensive circuit has been described which,in one form, will interrupt the operation of a relay for a predeterminedtime period or, in another form, will energize a relay for apredetermined time period, and which will insure one and only oneoperation for each actuation of the trigger.

What is claimed is:

1. A relay circuit comprising a series circuit of a resistor and acapacitor, a gas tube connected in parallel with said series circuit andhaving a cathode, an anode,

and a control element connected to apoint in said series circuit betweensaid resistor and capacitor, a relay having a winding connected inseries 'with'said gas tube,

means for applying a bias voltage to said control element comprising asecond resistor having one terminal connected to said control element, afirst switch under control of said relay and in series with said secondresistor, and a second switch connected between said cathode and anode.

2. A relay circuit comprising a series circuit of a resistor and acapacitor connected at a junction; a thyratron in parallel with saidseries circuit and having an anode, a control grid connected to saidjunction, and a cathode; a relay having a winding with two terminals,one of said relay winding terminals being connected to the saidthyratron anode; a switch responsive to said relay and having twoterminals; means for applying a voltage bias to said thyratron gridincluding a second resistor connected between said junction and one, ofsaid switch terminals; and a second switch connected to initiate currentflow through said relay winding when said second switch is closed. 1

3. A relay circuit comprising a series circuit of a resistor and acapacitor connected at a junction; a thyratron in parallel with saidseries circuit and having an anode, a control grid connected to saidjunction, and a cathode; means providing an anode to cathode circuit forsaid thyratron; a relay having a winding with two terminals, one of saidrelay winding terminals being connected in the said thyratron anode tocathode circuit; a switch responsive to said relay and having twoterminals; means for applying a voltage bias to said thyratron gridincluding a second resistor connected between said junction and one ofsaid switch terminals; and a second switch connected in said anode tocathode circuit.

4. A relay circuit comprising a relay including a winding having oneterminal for connection to a source of power and a second terminal, aswitch controlled by said relay and having a pair of terminals, aparallel circuit connected to said relay winding second terminal, saidparallel circuit comprising a thyratron having an anode, a cathode, anda control grid, a series circuit including a resistor and a capacitorconnected at a junction and further connected to said thyratron grid atsaid junction, and a second switch having two terminals, one of saidsecond switch terminals being connected to said cathode and the other ofsaid second switch terminals being connected to said relay windingsecond terminal, and means to apply a voltage bias to said thyratrongrid including a second resistor connected between one of said relaycontrol-led switch terminals and said junction.

5. A relay circuit comprising a relay including a winding having oneterminal for connection to a source of power and a second terminal, aswitch responsive to said relay and having a pair of terminals, aparallel network connected to said relay winding second terminal; saidparallel network having first, second and third junctions and includinga thyratron having an anode connected to said first junction, a cathodeconnected to said second junction, and a control grid connected to saidthird junction, a series circuit between said first and second junctionsincluding a first resistor and a capacitor connected together to providesaid third junction, and a second switch having two terminals, one ofsaid second switch terminals being connected to said first junction andthe other of said second switch terminals being connected to said secondjunction, and means for applying a voltage bias to said thyratron gridincluding a second resistor connected between said third junction andone of said pair of switch terminals.

6. A circuit as claimed in claim 5 wherein said series circuit resistorincludes a first resistor portion having a fixed resistance and a secondresistor portion having a variable resistance, said second resistorportion being connected between said first resistor portion and saidthird junction.

7'. A circuit as claimed in claim 6 characterized by the addition of athird switch responsive to said relay and also having two terminals, oneof said third switch terminals being connected to said first junctionand the other of said third switch terminals being connected to the saidone of said second switch terminals whereby said third switch isinterposed between said first junction and the said second switch.

8. A relay circuit comprising a first series circuit having first,second, and third junctions and including resistor means and capacitormeans serially connected to each other at said third junction, a firstparallel circuit having two branches, one of which includes a thyratronhaving an anode, a cathode, and a control grid and the other of whichincludes switch means for connecting said thyratron anode and saidthyratron cathode, a relay including a winding, second switch meansresponsive to said relay, and means to apply a biasing voltage, saidrelay winding being connected in series with said first parallel circuitto provide a second series circuit, said second series circuit beingconnected in parallel relation with said first series circuit at saidfirst and second junctions to provide a second parallel circuit, saidthyratron control grid being connected to said third junction, and saidmeans for applying a biasing voltage including said second switch meansand a resistor also connected to said third junction.

9. A relay circuit according to claim 8 wherein said relay winding has apair of terminals one of which is connected to said first junction andthe other of which is connected to said first parallel circuit.

10. A circuit as claimed in claim 8 wherein said resistor means includesa first resistor portion having a fixed resistance and a second resistorportion having a variable resistance, said second resistor portion beingconnected between said first resistor portion and said third junction.

11. A circuit as claimed in claim 10 characterized by the addition of athird switch means responsive to said relay and interposed between saidfirst switch means and said one branch of the said first parallelcircuit.

12. A relay circuit comprising a relay including a winding having twoterminals, a thyratron having an anode, a cathode, and a control grid,first and second switch means responsive to said relay, a third switchmeans, a first series circuit, a second series circuit, and means toapply a bias; said first series circuit having first, second and thirdjunctions and including a first resistor and a capacitor connectedtogether at said third junction, said control grid being also connectedto said third junction; said first resistor and said capacitor beingconnected between said first and second junctions; said second seriescircuit being connected in parallel with said first series circuit atsaid first and second junctions and including (1) said first and thirdswitch means connected in parallel, (2) a second resistor seriallyconnected between said parallel switch combination and said thyratronanode, and (3) a parallel combination of said thyratron and said relay,one of said relay winding terminals being connected to the saidthyratron anode and the other of said relay winding terminals beingconnected to the said thyratron cathode; and said means to apply a biasincluding a third resistor serially connected between said thirdjunction and said second switch means.

13. A circuit as claimed in claim 12 wherein said first series circuitfirst resistor includes a first resistor portion having a fixedresistance and a second resistor portion having a variable resistance,said second resistor portion being interposed between said firstresistor portion and said third junction.

14. A relay circuit comprising a first parallel branch, a secondparallel branch, said first and second parallel branches having firstand second junctions in common and said first parallel branch having athird junction, and first means for applying a bias; said first parallelbranch comprising a first series circuit connected between said firstand second junctions and including a first resistor and a capacitorconnected to each other at said third junction; said second parallelbranch comprising a second series circuit connected between said firstand second junctions and including, in series, a second resistor, afirst and a second switch means connected in parallel, and a parallelcombination, said parallel combination comprising two arms, one armincluding a thyratron having an anode, a cathode, and a control gridconnected to said third junction, the other of said arms including, inseries, a relay having a winding controlling said second switch means,and a second means for applying a bias; and said first means forapplying a bias including a third switch means responsive to said relayand a third resistor connected between said third junction and saidthird switch means.

15. A circuit as claimed in claim 14 wherein said first parallel branchfirst resistor includes a first resistor portion having a fixedresistance and a second resistor portion having a variable resistance,and said second resistor portionbeing interposed between said firstresistor portion and said third junction.

16. A relay circuit including a relay having a winding and a thyratronhaving an anode, a cathode, and a control grid, said relay beingconnected between said anode and said cathode, a first switch means forconnecting said anode to a source of power, a series circuit connectedto said cathode, said series circuit comprising a capacitor and aresistor joined at a junction, said control grid being connected to saidjunction, and a means to apply a bias to said control grid connected atsaid junction and including a second resistor and a switch meanscontrolled by said relay.

17. A relay circuit comprising a series circuit of a resistor and acapacitor connected at a junction; a thyratron in parallel with saidseries circuit and having an anode, a control grid connected to saidjunction, and a cathode; means providing anode to cathode circuits forsaid thyratron; a relay having a winding with two terminals, one of saidrelay winding terminals being connected in one of said thyratron anodeto cathode circuits; a switch responsive to said relay and having twoterminals; means for applying a voltage bias to said thyratron gridincluding a second resistor connected between said junction and one ofsaid switch terminals; and a second switch connected in one of saidanode to cathode circuits.

.No references cited.

